STUDIES OF NATURAL POPULATIONS OF MUS.: III. COAT COLOR POLYMORPHISMS

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Abstract
Samples of natural populations of house mice, Mus musculus, from southeastern Michigan, were examined for coat color polymorphisms. To uncover recessive alleles, wild mice were mated with laboratory mice homozygous for a number of recessive coat color alleles, and the offspring backcrossed on the wild parent. The former procedure did not reveal any heterozygosity at the color loci in the wild mice tested (82 animals tested for 7 loci) whereas the latter uncovered in one wild mouse what appears to be a recessive gene concerned with extensive belly spotting. No further genetic information is available because of poor viability of the affected mice. The rarity of recessive coat color alleles was attributed to a combination of small sample size, population subdivision (inbreeding) and selection against homozygotes. A polymorphism involving the Aw and A alleles at the agouti locus was also found. The overall frequency of A was 0.85 [plus or minus] .011. Breeding data permitted the calculation of the allelic frequencies at the agouti locus without resorting to an assumption of random mating. When observed zygotic frequencies were compared with those expected under random mating a deficiency of heterozygotes was observed. This deficiency could be explained by assuming an inbreeding coefficient of 0.18, a value obtained from other sources. White spotting on the ventrum, a characteristic under polygenic control, was observed in all but 1 of the samples studied. No attempt was made to analyze the spotting data.